Because it's such a clear-cut and inarguable case of an actual issue, that whilst largely solvable, shows that there are people here (including you two) who have such an elevated threshold for what qualifies as a "problem" with compatibility that discussing the problems is nearly impossible, because you'll just outright deny they exist, no matter how demonstrable they are. Denying things are demonstrably problems (even if solvable - which hopefully all are!) are problems is utterly toxic to any kind of reasonable discussion.
It's not a disagree thing. It's that you're outright dismissing things which are problems, and you know are problems, because they're solvable.
Claiming that a molehill is a mountain doesn't make it so. Again, you're presuming that people will want to play 2014 classes in a 2024 game. Right there, the problem largely solves itself over a fairly short time because, frankly, most people are just going to move on to the newer versions of the class, same way they moved on with errata'd versions of the class that came up from time to time. Moving a class power from one level to another is such a minor issue that no one is going to massively freak out over it.
But, even in a group that does mix their classes between 2014 and 2024, why would it be a problem? Very, very few groups have multiple players playing the same class, so, why would you care when Dave get's his ability? His character is different from yours. Ok. And?
Since the classes, in either version, are not terribly different power wise, can be used in the same adventures without any real problem, and don't step on each other's toes, your definition of an "actual issue" seems to be setting threshold for what is considered a "problem" very, very low. People who have ACTUALLY tested this in play are telling you, flat out, that this hasn't been an issue. Yet, you insist that their experience cannot possibly be true because you have identified an "actual issue".
And you wonder why people are getting dismissive?